Well here's my 2 cents worth.
First as far as the 44's go. I have been running a stock (rebuilt but with stock parts) Scout 44 rear in my 75 Scout II since I built it about 5 years ago. I have pulled it down every fall to get a good look at the shafts and there is no twist on the shafts yet. I am in the process of building a FF 60 rear for the Scout though. I guess I'm doing it because I have one that was free and it's time for something new.
As far as the 44 front goes. Again I am running stock shafts ( with Spicer 5-760X joints) and again no breakage.
I run a 350 Chev with an SM-465 trans and a 205 case. There are 4.10:1's in the diff's and 35" MT\R's.
Trails (of note) so far are Rusty Nail, Gold Bar Rim, Hell's Revenge, Hole in the Rock (including the Rincon) and the Hanging Tree. Now I am an old guy and I tend to finess a little more than some, but it has seen it's share of wide open throttle as well. Go to Moab and you will see tons of Rubicons running around with stock 44's and 35" tires. Keeping in mind that the Rubicon 44 front is not going to take as much abuse as a standard 44 front from a Scout, Chev, Ford etc.
As far as breaking things goes, I guess you could break a hardened 60, a 14 bolt rear or just about anything else if you try hard enough. Like I was told once, there are guys who could break a crowbar in a sandbox if you let them.
Concerning the truck though. I would leave it as a street truck, it looks sweet. You can build anything into a 4X4 and wheel it. That can't be said for coming up with straight old iron like that.